Ivan Marcano has returned to Porto just one season after leaving for Serie A side Roma.
Marcano left Porto in May 2018 on a free transfer following four years with the Primeira Liga team, signing a three-year contract with the Giallorossi.
However, the centre-back managed just 13 appearances across all competitions in 2018-19, and has now returned to Portugal, with Roma receiving a €3million fee.
The 32-year-old has agreed a four-year deal with Porto - who sold defender Felipe to Atletico Madrid earlier in the off-season - keeping him at Estadio do Dragao until 2023.
Marcano's departure leaves Roma short of options in central defence, with Kostas Manolas having joined Serie A rivals Napoli.
Toby Alderweireld, who has one year left on his current Tottenham contract, is reportedly a target for Roma, who on Wednesday signed goalkeeper Pau Lopez from Real Betis, having already brought in Leonardo Spinazzola and Amadou Diawara.